Bottlenose dolphins of the Archipelago of Bocas del Toro, Panama

Boat traffic effect on behavior

Kassamali-Fox. A., Christiansen, F., Quinones-Lebron, S., Rusk, A., May-Collado, LJ, and B. Kaplin. Using Markov chains to model the impacts of the dolphin watching industry on the dolphin community of Dolphin Bay, Bocas del Toro, Panama. International Whaling Commission 2015. SC/66a/WW11.​Boat-based tourism activities are concentrated in Dolphin Bay due to the high site fidelity of dolphins in this area and its potential importance as a calving and nursery ground for females. Many of the individuals routinely exposed to tour boats are females with dependent offspring. Previous tourism impact studies at this site show that tour boats elicit short-term changes in dolphin behavior and acoustic structure, however, the relationship of these responses to the population’s biology and ecology is not clear. Animal behavior is temporally dynamic, therefore, assessing the effects of potential impacts on the time structure of behavior, such as behavioral transitions and time-activity budgets can provide useful information about the biological significance of anthropogenic disturbance. Because the time-activity budget is tied to the energy budget of individuals, information on the former can provide useful information about the energetic costs oftourism to a population. In this study, the behavioral transitions of focal dolphins in Dolphin Bay, Bocas del Toro were analyzed using transition matrix models, a time sequencing analytical technique now widely applied to dolphin behavior to explore the potential impacts of tourism on cetaceans. First-order, time discrete Markov chain models were used to assess the effect of tour boat activities on dolphin behavioral transition probabilities in both control and impact scenarios. The effect of boat interactions was then quantified by comparing transition probabilities of both control and impact chains. Data were also used to construct dolphin activity budgets. Additionally, a Generalized Log Linear Mixed Model (GLMM) was fitted to a subset of the data containing only females with dependent calves to assess the effects of tour boats on this vulnerable age-sex class. The Markov chain analysis revealed that in the presence of tour boats, dolphins were less likelyto stay in a socializing state and were more likely to begin travelling, and were less likely to begin foraging while in a traveling state. Additionally, the time-activity budgets showed that foraging decreased as an effect of tour boat presence, and traveling increased, indicating a shift in the important relationship between these two activities. The results of the GLMM showed that females with dependent calves are less likely to forage and more likely to travel when tour boats are present. These behavioral responses are likely to have energetic implications for individuals through two possible mechanisms: reduced energy acquisitionand increased energy expenditure. The effect of lost foraging opportunities and increased physical demands may be more pronounced for nursing females whose physiological demands are higher and can potentially lead to poor reproductive outcomes and reduced fitness of individuals. Tour operator compliance with the ARAP No. 2007 Resolution on number and frequency of tour boats interacting with dolphins in Dolphin Bay, as well as approaching distance to females with calves is urgently needed to minimize potential longterm impacts on this small, genetically distinct population.

​Our previous work shows that dolphins significantly respond to DW boat presence by modifying their whistle frequency and duration particularly whenengaged in foraging activities. The usual assumption is that the noise associated with the DW boats is responsible for the change in whistle parameters. In this study we evaluate the effect of noise levels on whistles acoustic structure by analyzing recordings obtained in 2007, 2008 and 2012 under various boat interactions. We measured ambient noise levels (RMS values, 100Hz to 48kHz) for each of these recordings and for each whistle within those recordings we measured a number of standard frequency variables and duration. Noise levels increased with boat presence; however, there was also significant variation among years. After adjusting the level of significance for multiple comparisons to α= 0.006, our results indicate that 8% of the variation in whistles minimum frequency is explained by the interaction between noise levels and year. In contrast, 16%, 22%, and 11% of the variation in whistle ending frequency, peak frequency, and duration was explained by year, respectively. In agreement with recent studies these results indicate that while annual variations in noise levels can significantly affect dolphin communication, dolphins show great plasticity in coping with these changes. Furthermore, it is important to highlight that changes in noise levels only explained a small percent of the variation observed in dolphin whistle structure suggesting that other cues (e.g., mode of approach) and other sensory modalities (e.g.,vision) associated with these boat-dolphin interactions may be more important contributors to changingdolphin acoustic behavior.